PERTURBATION OF NUCLEOSOME STRUCTURE BY THE ERYTHROID TRANSCRIPTION FACTOR GATA-1

The ability of transcription factors to gain access to their sites in chromatin requires the disruption or displacement of nucleosomes cover ing the promoter, signalled by the generation of a nuclease hypersensi tive site. We characterise here the alterations in nucleosome structur e caused by binding of the erythroid factor GATA-1 to a nucleosome car rying GATA-1 sites. DNase I and micrococcal nuclease probes show that GATA-1 binding causes extensive, cooperative breakage of the histone/D NA contacts to generate a complex very similar to that formed by the f actor with free DNA. The only region which differs is confined to abou t 50 bp surrounding the nucleosome dyad axis which appears to be the d omain of residual contact between the DNA and histone octamer. Despite considerable breakage of the histone/DNA contacts, the complex is com pletely stable in solution, and disruption of the nucleosome is entire ly reversible: it is regenerated quantitatively upon removal of the tr anscription factor. Moreover, the histone 2A/2B component of the octam er does not exchange to external competitor. We suggest that formation of this complex may be a step in the generation of a fully hypersensi tive site in viva over regulatory elements containing GATA family bind ing sites. (C) 1998 Academic Press Limited.